Investigate and fix failing unittests

[twiecki]

FAIL: test_gsl_blas_zherk (test_blas.BlasTest)

Traceback (most recent call last):
File "cython_gsl/test/test_blas.py", line 228, in test_gsl_blas_zherk
self.assertAlmostEqual(x,0, 14)
AssertionError: -1.6000000000000001 != 0 within 14 places

FAIL: test_gsl_linalg_LU_refine (test_linalg.LinalgTest)

Traceback (most recent call last):
File "cython_gsl/test/test_linalg.py", line 24, in test_gsl_linalg_LU_refine
self.assertAlmostEqual(x,0, 15)
AssertionError: 5.820766091346741e-10 != 0 within 15 places

FAIL: test_gsl_atanh (test_math.MathTest)

Traceback (most recent call last):
File "cython_gsl/test/test_math.py", line 118, in test_gsl_atanh
self.assertAlmostEqual(mathgsl.t_gsl_atanh(1.3),0, 16)
AssertionError: nan != 0 within 16 places

FAIL: test_gsl_frexp (test_math.MathTest)

Traceback (most recent call last):
File "cython_gsl/test/test_math.py", line 125, in test_gsl_frexp
self.assertAlmostEqual(t[0],0.6, 16)
AssertionError: 0.0 != 0.6 within 16 places

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Ran 328 tests in 3.849s

FAILED (failures=4)